When a Li-ion battery is used as a power supply, the voltage of the battery end will drop from 4.2V to 3.3V during the discharging process. Therefore, a voltage regulator is needed to regulate the battery voltage to a stable voltage for supplying to an electronic product. Hence, a low dropout regulator is most suitable for this purpose under the premise of reducing volume.
However, conventional low dropout regulators, such as that disclosed in Taiwan Patent No. 200534070, often require external load capacitors to stabilize and boost transient response. Therefore, it has become a critical issue of developing a low dropout regulator that does not require external passive elements or requires only very few number of passive elements. For example, the following articles all discuss similar low dropout regulators:
[1] IEEE Trans. on Circuits and Systems I: Regular Papers, Vol. 55, No. 5, pp. 61392-1401, June 2008;
[2] IEEE J. of Solid-State Circuits, Vol. 38, No. 10, pp. 1691-1702, October 2003; and
[3] IEEE J. of Solid-State Circuits, Vol. 40, No. 4, pp. 933-940, April 2005.
However, all of the low dropout regulators proposed in the above articles may not be applied to a power supply with a relatively large input range.
It is therefore tried by the inventors to develop a low dropout regulator that is designed to use a Li-ion battery as a power supply input, and to provide a stable voltage source given different load changes without any external load capacitor when working under different voltage inputs.
The present invention may effectively reduce the chip manufacturing cost and be integrated on a chip easily. The present invention is an improved no-load-capacitor low dropout regulator. A preferred embodiment of the low dropout regulator according to the present invention has been implemented in a typical CMOS process.